This invention relates to a hermetic case for mounting a circuit board and an electronic circuit apparatus using above hermetic case, for use, for example, in an automotive ignition timing control system of an internal combustion engine.
FIG. 8 illustrates one example of a conventional electronic circuit apparatus for use in an automotive ignition timing control system. In FIG. 8, reference numeral 1 designates an electronic circuit board having electronic components la thereon, 2 designates a case body including a case main body 2a mounting the circuit board 1 therein, 3 designates a channel formed in a surrounding edge of the case main body 2a, 4 designates a lid for covering the case main body 2a, 5 designates a folded edge at a surrounding edge of the lid 4, and 6 designates an epoxy resin filler filled between the folding part 5 and the channel 3.
In order to prevent moisture in the ambient atmosphere from causing any adverse effect on the electronic components 1a on the circuit board 1 within the case body 2, the ease main body 2a and the lid 4 are made of a plastic material and are hermetically sealed by the epoxy resin filler 6. Also, the circuit board 1 is securely attached to the plastic main body 2 by means of screws 7.
In the electronic circuit apparatus as described above, pressure within the sealed case 2 changes with the temperature of the ambient atmosphere changes, which can range from -40.degree. C. to 120.degree. C. As this pressure fluctuation occurs repeatedly, the case 2 composed of the case main body 2a and the lid 4 can to crack, and ambient moisture and rainwater can enter into the interior, of case 2 thereby damaging the electronic components.
Also, because of the repeated pressure fluctuation, the case body 2 and the electronic circuit board 1 are repeatedly deformed and bent. This causes the solder connections between the circuit board 1 and the electronic components 1a to be damaged.